Thoughts on Mugello 186 port timings

[Grumpy225]

Building up a new Mugello 186 and ran into what I think is a potential problem

the port timings are such

Exhaust 180
Transfer 126
Intake 156

Top of exhaust port to top of cylinder 34.78mm
Top of transfer to top of cylinder 48.4mm
Piston crown to top of cylinder 2.58mm
Squish 1.65mm
Piston sits .48mm below the exhaust and transfer ports

No work has been done on the cylinder ports
Case is an Eibar spanish block matched to the cylinder (spigot height problem maybe?)
58/107 crank
22 Dellorto
Evergreen big bore exhaust
Varitronic
Spanish LI150 Special gear box (with the big jump between 3rd and 4th) <- not my choice but that's what was given to me for the build


So if I read these right the port timings are really set up for a motor that's going to be turning 8000 rpm or so. I don't think that in its current configuration that this will make the power it should. The plan is for a touring motor with lots of freeway miles.

Any help would be much appreciated.

[ulyssescale]

There isn't much bad about those port timings. Obviously the squish a bit larger than I'd like to see. Are you running a head gasket?

Personally, I would stretch it out a bit by using a longer rod. You'd be able to make changes to the ports to put them where you need them, whereas because you can't lower the barrel anymore (unless you have a thick gasket at the base) and if you raised the barrel you would have to spend some money to do something with that head (machine the gasket face so the head sits into the barrel).

I would toss that gearbox. I ran a Spanish 150 box like that and I could only get into 4th going down a damn hill.

I mean, if you are aiming for power at 8,000 rpm when will you be hitting that rpm figure? Probably only in 3rd gear - and you still would lose everything shifting into 4th gear. Ditch that gearbox.

[Grumpy225]

Right now there is no headgasket. I am at the measuring everything out stage.

Aggreed about that gear box but it's not my decision. Already talked to the owner they said they wanted it.

If I have .48mm taken off the bottom of the cylinder that would bring the squish down to 1.17mm and line up the piston at bdc with the ports. The only problem I can see would be getting a good squish and run a head gasket.

Sound reasonable?

[holty]

i was thinking remove material from the bottom of the barrel to gain more torque and to get a good squish,i did the same thing to my ts1 and it made a big improvement in the bottom end power, if you cant use a gasket on the head, machine a groove and use an o-ring instead maybe ?
holty

[wack 63]

You could not use a base gasket and seal it with Threebond and because the head sits in the bore just use Wellseal on the head. Pretty sure there are various thicknesses of head gasket supplied in the kit should you need one to set the squish.

[Grumpy225]

Case spigot measured out almost identical.

Spanish 29.67mm
Italian dl 125 29.88

If I pull the base gasket (lower the barrel) inlet timing goes up by 1 degree and exhaust goes down 1. Interesting stuff here.

[ulyssescale]

Personally, I would rather a lower exhaust figure, like 176-178. That exhaust pipe won't create anything useful at 8,000rpm, will it? The only reason for that rpm figure is to make that gearbox doable?

Lower the barrel, or get an expansion pipe or go with a different gearbox. Seems like a mix of parts that are going to be forced to work together. Interstate 25 and 80 isn't a putt-putt route.

[Grumpy225]

I've been doing a lot of research on this and found the 8k point is where it will make it's peak power with the 180 exhaust port. Just for grins I threw a 2.9mm packing plate under the cylinder and came up with these port timings

Exhaust 170
Transfers 140
Intake 149

Everything i've been reading tells me that 140 transfers are pretty much bad news. Which is too bad since the other two are closer in line to actually working.

[ulyssescale]

Is there any research that shows the Ancillotti exhaust at 8,000 rpm? I stuck that into the gearing calculator with that Spanish gearbox. Maybe I've forgot what fun looks like on paper?

[Grumpy225]

I found this on the exhaust

http://www.lambretta.it/foto_gestione/p ... llotti.pdf

Not really useful since it's mapping mph to bhp. Ideally rpm to bph but who cares at this point. I took the peak speed and checked against the scooterhelp gearing calc with the gearbox I'll be using.

It peaks according to their graph somewhere around 6.5k That sounds like about what I expected.